For mature communities, it might be regular members. Without them, activity would fizzle out quickly. If they visit the community and see too many 'newbie' threads, or repeatedly asked questions, they might begin to visit less frequently. That soon becomes a problem.

To cater to regulars, you might make regular references to key members, previous events/activities, and ensure the balance of discussions are about things that go beyond the basics.

In this situation, you assume that most members know what came before.

However, if the community has a growth problem, you might focus upon newcomers. Not just people new to the community, but new to the topic.

Imagine you've just begun fishing. You need some equipment advice. You find a and join a fishing community. When you join do you want to see discussions about obscure/new fishing techniques, or do you want to get the basic equipment information. Yet, after a few years in that community, you probably don't want to see the same entry level equipment discussions anymore.

These are two ends of a wide continuum. You need to shift the balance to suit your community. It might be 70/30 split towards regulars, or 30/70 to newcomers. It's your choice.

It helps to have a good design, groups, and ensure everyone can find what they need. However, being easy to find isn't the same as influencing what people see when they first visit, what appears in the communications, and how you spend more of your time.